1. (Field of the Invention)
The present invention relates to an acoustic characteristics changing device and, more particularly, to an acoustic characteristics changing device which can electrically control passive characteristics with respect to an acoustic energy.
2. (Description of the Prior Art)
As a technique of this field, an acoustic panel and an acoustic switch are known. Examples of the acoustic panel are disclosed in Japanese Utility Model Publication No. sho 54- 4334, and Japanese Utility Model Application No. sho 61-32910. According to the former example, an acoustic panel in which a reflection material is attached to the front surface and a sound absorption material is attached to the rear surface is reversed, so that the acoustic panel can be selectively used as the reflection panel and the sound absorption panel. According to the latter example, a pivotal door is arranged on the front surface of a sound absorption panel, and is pivoted to finely adjust acoustic characteristics of the panel as a whole. On the other hand, as the acoustic switch, keys of wind instruments or the like are known. When a sound insulation material is moved in an acoustic path, an acoustic impedance can be switching-controlled between an infinite level and zero.
However, the conventional acoustic characteristics changing device controls the acoustic impedance by mechanically moving the sound insulation material along the acoustic path or mechanically switching between an acoustic reflection member and an acoustic transmission member. For this reason, the mechanical switching mechanism is complicated, and it is not easy to finely adjust passive characteristics with respect to an acoustic energy. Furthermore, even when a sound absorption factor can be changed to some extent, a sound absorption frequency cannot be controlled.